Envelope Size Calculator
Find the envelope that fits a finished card, with the clearance it needs, and check the thickness against the postage bands.
At a glance
- What you enter
- Card width, Card height, Card thickness, Clearance per side, Inserts and embellishments, Envelope weight
- What you get
- Envelope width needed, Envelope height needed, Envelope width needed, Envelope height needed, Nearest trade envelope size, Envelope weight chosen, Filled thickness, Filled thickness, Within the thin letter band, Within the large letter band, Likely treated as a parcel, Gusseted or board backed envelope advised, Card can be turned inside the envelope, Extra clearance suggested for a square card
- Formula shown
- Yes, every step, right below your results.
- Cost and privacy
- Free, no account needed, and nothing you type is stored.
See worked examples ↓ Read the FAQ ↓ Share this calculator ↓
Results are estimates for general information only, always verify with a professional or official source before acting on them.
How to use the Envelope Size Calculator
- 1 Enter Card width (mm), The shorter side of the finished card.
- 2 Enter Card height (mm), The longer side of the finished card.
- 3 Enter Card thickness (mm), One gsm is about one thousandth of a millimetre for uncoated card, so 300 gsm is about 0.3 millimetres.
- 4 Enter Clearance per side (mm), Two to three millimetres per side suits most cards. A square card, or one with depth, wants more.
- 5 Enter Inserts and embellishments (mm), Anything inside the envelope besides the card: a ribbon, a badge, a second card, tissue.
- 6 Enter Envelope weight, A heavier card needs a heavier envelope or it creases in the post.
- 7 Press Calculate. You get Envelope width needed, Envelope height needed, Envelope width needed, Envelope height needed, Nearest trade envelope size, Envelope weight chosen, Filled thickness, Filled thickness, Within the thin letter band, Within the large letter band, Likely treated as a parcel, Gusseted or board backed envelope advised, Card can be turned inside the envelope, Extra clearance suggested for a square card, and every intermediate step stays visible under "How is this calculated?"
- 8 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.
Worked examples
Real numbers run through this calculator. Open any example to load it into the form above and change it.
An A6 card in a C6 envelope
The standard handmade greeting card, single card, no embellishment.
You enter
- Card width
- 105 mm
- Card height
- 148 mm
- Card thickness
- 0.30 mm
- Clearance per side
- 2 mm
- Inserts and embellishments
- 0 mm
- Envelope weight
- 2
You get
- Envelope width needed
- 109.00 mm
- Envelope height needed
- 152.00 mm
- Envelope width needed
- 4.29 in
- Envelope height needed
- 5.98 in
- Nearest trade envelope size
- 1
- Envelope weight chosen
- 100.00 gsm
- Filled thickness
- 0.45 mm
- Filled thickness
- 0.02 in
- Within the thin letter band
- 1
- Within the large letter band
- 0
- Likely treated as a parcel
- 0
- Gusseted or board backed envelope advised
- 0
- Card can be turned inside the envelope
- 1
- Extra clearance suggested for a square card
- 0.00 mm
An envelope of 109 by 152 millimetres, which is inside the C6 range. Filled thickness about 0.45 millimetres, so a standard letter.
A 5 x 7 in card with a ribbon
A larger card with a ribbon bow that adds four millimetres of depth.
You enter
- Card width
- 127 mm
- Card height
- 178 mm
- Card thickness
- 0.35 mm
- Clearance per side
- 3 mm
- Inserts and embellishments
- 4 mm
- Envelope weight
- 3
You get
- Envelope width needed
- 133.00 mm
- Envelope height needed
- 184.00 mm
- Envelope width needed
- 5.24 in
- Envelope height needed
- 7.24 in
- Nearest trade envelope size
- 3
- Envelope weight chosen
- 120.00 gsm
- Filled thickness
- 4.50 mm
- Filled thickness
- 0.18 in
- Within the thin letter band
- 1
- Within the large letter band
- 0
- Likely treated as a parcel
- 0
- Gusseted or board backed envelope advised
- 1
- Card can be turned inside the envelope
- 1
- Extra clearance suggested for a square card
- 0.00 mm
An envelope of 133 by 184 millimetres, which is the A7 envelope size exactly. The ribbon still keeps the package well inside the letter band.
A square card with a badge
A 140 millimetre square card with a metal badge inside, which is the awkward case.
You enter
- Card width
- 140 mm
- Card height
- 140 mm
- Card thickness
- 0.40 mm
- Clearance per side
- 5 mm
- Inserts and embellishments
- 6 mm
- Envelope weight
- 4
You get
- Envelope width needed
- 150.00 mm
- Envelope height needed
- 150.00 mm
- Envelope width needed
- 5.91 in
- Envelope height needed
- 5.91 in
- Nearest trade envelope size
- 3
- Envelope weight chosen
- 250.00 gsm
- Filled thickness
- 6.55 mm
- Filled thickness
- 0.26 in
- Within the thin letter band
- 0
- Within the large letter band
- 1
- Likely treated as a parcel
- 0
- Gusseted or board backed envelope advised
- 1
- Card can be turned inside the envelope
- 1
- Extra clearance suggested for a square card
- 3.00 mm
Six and a half millimetres of contents, so this crosses the thin letter band and a board backed envelope is the sensible choice.
Guides that go with it
Standard Paper Sizes for Crafts and Handmade Projects
If you are pricing a paper project, the honest headline is this: most small handmade paper projects cost somewhere between a few dollars and about $30 in materials, and a bigger run of cards, journals...
How Much Fabric Do You Need for Your Sewing Project?
You can work out your fabric requirement in about 15-30 minutes with a tape measure, your pattern, and a bit of arithmetic. By the end of this guide you will know how to read a pattern envelope, measu...
The Complete Handcraft Measurement Guide for Beginners
If you are new to crafting, measuring is usually the first place things go sideways: a cut is 3 mm short, two "identical" squares are not identical, or a pattern that looked fine on paper does not fit...